How Do Disc Brakes Work?

April 28, 2022

new car disc brake in workshop.

Understanding how a brake disc works would enable you to see more the importance of brakes. A disc brake, of course, is one type of brakes. It makes use of calipers that squeeze pairs of pads against a rotor or a disc to create the necessary friction to make the car stop. This action slows down the shaft’s rotation. It reduces the rotational speed of the shaft or makes it stop completely. Thus, when you step on the brake, the car either slows down or stops.

The disc brake, of course, is an integral component of the brake system. Yet, it is actually the part of the brake system that stops the car. Brake disc has different types. But the most common type is that of the single-piston floating caliper. The common form of brakes used for motor vehicles, however, is the hydraulically actuated.

Mechanism & Functions of Disc Brake

The brake system has the brake rotor, which is the rotating part of the system. The disc brake works against this rotor (brake disc). The disc brake is usually made of gray iron—a certain form of cast iron. 

Different disc brakes have varying designs. Some have solid built. Others have designs with hollowed-out fins and veins that join the two contact surfaces of the disc. These hollowed-out designs are often necessary, depending on the power and weight of the vehicle. 

Benefits of Using Disc Brake

There are many advantages to the use of disc brakes. First, it is lighter than the drum brakes. Second, it is capable of better cooling, having its braking surface exposed to air. It is also capable of resisting fade as compared to other types of brakes.

Moreover, it offers a uniform pressure distribution. Plus, the brake pads of this type of brake can be easily replaced. Lastly, this type of brake is designed to self-adjust.

On the other hand, it also fraught with disadvantages. First, it is more expensive than drum brakes. It also requires higher pedal pressure to stop a vehicle. Moreover, it doesn’t exhibit any servo action. Lastly, it is not easy to equip with an appropriate parking attachment.  

Types of Disc Brakes

Slotted Vs Drilled Discs

Ventilated discs are usually meant to dissipate the heat generated by friction. These ventilated discs are more often used on the front discs. This is because the front discs are more loaded. If you would look at the discs of many cars, motorcycles, and bicycles, you’ll notice that their discs have slots or holes. These holes or slots are meant to dissipate heat, reduce noise, aid in surface water dispersal, and reduce mass. Moreover, slotted discs feature shallow channels that are machined into the discs. These shallow channels help in removing gas and dust. 

In the arena of racing, slotting is the more preferred method because it helps in removing gas and water. It also deglazes brake pads. Slotted discs, however, are not often used for standard vehicles. The reason is that they quickly wear out brake pads. 

Some discs, however, come with both slots and holes. Both drilled and slotted discs bring in some benefits in wet conditions. This is because the holes and slots prevent the onset of a buildup of water between the pads and the disc. 

Two-piece Discs (Rotors)

The two-piece discs are a type of disc wherein the disc’s center mounting is separately manufactured from that of the outer friction ring. The central section is often used for fitment and is often called “bell” or “hat.” It is generally made of alloy (7075 alloys) and has been hard anodized to have a lasting finish. The outer disc ring, however, is made of grey iron, though some are built of steel. The two-piece discs are first used in Motorsport. But now, it is common also among high-performance applications as well as aftermarket upgrades.

The main advantage of a two-piece disc is it helps save in critical unsprung weight. Another advantage is that it helps in dissipating heat from the surface of the disc via its alloy bell. 

The two-piece disc, moreover, can either be fixed or floating. The floating disc features a complicated floating system. It comes with drive bobbins that let the disc’s two parts to contract and expand at different rates. This lessens the percentage of disc’s warping from overheating. The floating disc, however, tends to rattle and collect debris. It is, therefore, best for Motorsport. 

Major Components of Disc Brake

The disc brake features several main components. These components include the brake pads, caliper with piston, a rotor that is mounted to the hub, and the piston and cylinder. If you haven’t seen a disc brake before, you can try to imagine a bicycle brake that has a caliper. This caliper squeezes the brake pads towards the wheel. 

Similarly, the brake pads do the same dynamics with the rotor. The rotor is squeezed by the brake pads. The force that lets the brake pads to squeeze the rotor is transmitted hydraulically. The friction between the disc and the pads slows down the disc. 

The car has momentum (kinetic energy) when it is moving. The brakes then need to take out this energy for the car to stop. The brakes do this by converting kinetic energy to heat energy. Heat energy needs to be dissipated so that the brakes and the disc will not break down. Hence, the disc needs to be vented. Vented disc brakes feature vanes between both sides of the disc. These vanes allow air through the disc to cool it. Here are the different parts of the brake discs:

1) Brake Disc (Rotors)

The disc brake system will never be complete without the brake disc. One of the main components of the disc brake system is the brake disc. It is a very important part of the disc brake system and is mounted on the hub. The hub comes in contact with the disc, and their contact surface should be clean. Otherwise, the disc will wobble side-to-side. Moreover, if the disc surface is damaged or rusted, the force of the brake will be reduced. 

The disc may undergo uneven warp or wear, especially if there is warp or rust after it overheats. Hence, the thickness of the brake disc’s surface usually differs. You’ll know if the disc has uneven wear if the steering wheel shakes when you step on the brake pedal or when the brake pedal pulsates. You can have the brake disc surface machined to rectify this problem. 

You can bring your car to a mechanical shop to have the working surface of the disc inspected. If you could have it machined, then, have it machined. Manufacturers of brake discs, of course, set the minimum disc thickness. If the disc has not yet reached the minimum thickness allowance, then, it could still be machined. However, if the disc is already so much worn out beyond repair, then you need to replace it. 

2) Brake Pads

The brake pads are usually made of friction material that is molded tightly to the metal backing plate. Their primary function is to stop the rotation of the disc. Hence, they should have the necessary friction material to make the disc stop. Many cars have their backing plate equipped with noise-reducing shims aside from brake pads. 

The friction material, however, has a specific minimum thickness. This minimum thickness is specified by manufacturers. If this thickness has been breached, then you need to replace the pads, for it is beyond repair. 

Brakes are essential to safe driving. But if any of the brake pads inside the caliper bracket seizes up, it may cause a handful of problems. It may lead to uneven wear of the brake pads, noise, and overheating. So, if the pads are already uneven wear, you need to replace them. When replacing brake pads, you need to replace them as a set.

3) Brake Calipers

The brake system also has the brake calipers. These calipers are usually mounted on the steering knuckles. The rear calipers are bolted or attached to the rear spindles. They are also attached by the caliper slider pins in such a way that it allows the calipers to move laterally. This lateral movement is critical to the operation of the brake. If the caliper pins prevent this lateral movement, then, the caliper may overheat. 

If this sticking problem is noticed earlier, then there is a greater chance of saving the calipers from further damages. You can have the slider pins restored in such a case. Yet, if you can’t free a seized caliper pin, then you need to replace the whole caliper. 

For this reason, you need to have the brake system checked regularly. Mechanics usually lubricate and clean caliper slider pins when you have your car serviced. But make sure to have the caliper replaced if it exhibits any problem. 

4) Pistons and Cylinders

Disc brakes have different designs. But the most common design makes use of a single hydraulically actuated piston in a cylinder. Some high-performance brakes, of course, make use of many pistons up to a maximum of twelve. 

Contemporary cars make use of various hydraulic circuits. These hydraulic circuits actuate brakes on every set of wheels. This is done for safety measures. Moreover, the hydraulic design allows for increasing the force of the brake. 

Pistons are also referred to as “pots.” So, you will often hear, “how many pots does each caliper house?” Don’t be confused if you hear this question, for it only means the number of pistons housed by a caliper. 

Pistons may sometimes fail to retract. This usually happens when you’ve stored your car outdoors under adverse conditions. Moreover, the piston seals may leak once your car reached high mileage. In such cases, you should have these problems immediately rectified.